This invention relates generally to power supplies for electronic systems.
Electronic equipment requires a source of electrical power. Typically, AC power is converted to at least one DC voltage at a level required by the electronic equipment. In large electronic systems, for example, telecommunications systems and large computer server systems, it is common to provide multiple power supplies, operating with outputs in parallel. It is also common to provide redundant power supplies to ensure continuous operation even with the failure of one or more power supplies. For example, in the telecommunications industry, if N power supplies are needed, it is common to use N+1 power supplies. It is also known to provide two separate sources of AC power, with separate banks of power supplies on each source of AC power, to ensure continuous operation even with the failure of one AC power source. For example, in large computer server systems, if N power supplies are needed, it is known to provide two different AC power sources with N+1 power supplies on each AC power source (2N+2 total power supplies with outputs in parallel). Alternatively, at least one isolated DC voltage may be distributed, and multiple local DC-to-DC converters may operate in parallel to provide the voltages and currents needed by each local system.
The number of power supplies operating with parallel outputs is typically determined by worst-case current load requirements. For example, if a system requires 100 amps maximum, and each power supply can provide 10 amps maximum, then at least 10 power supplies are connected to operate with outputs in parallel. If the actual current load is less than the worst-case current load, then each power supply provides some fraction of the maximum design current per power supply. Power supply redundancy may result in each power supply providing a relatively small fraction of the maximum design current per power supply. In general, within the designed range of output current, individual power supply efficiency improves with increasing output current. Power supply redundancy may result in each power supply operating at a reduced efficiency. For example, in a system with two power sources and 2N+2 power supplies, if both power sources are available, and if all power supplies are operational, then N+1 supplies are redundant, and each individual power supply is providing less than 50% of its maximum output current. There is a need for more efficient operation of power supplies configured with parallel outputs.
Output current is monitored for at least some power supplies. The number of power supplies providing current is then controlled to improve the overall system efficiency. For example, when the output current of one or more individual power supplies falls below a threshold, one or more power supplies may be placed into a standby mode. This increases the output current of the power supplies that are in an operational mode, improving their efficiency. If the current load increases, one or more supplies in standby mode can be rapidly switched to an operational mode. Optionally, a controller may also turn some power supplies completely off (or offline), as opposed to just switching to a standby mode, further conserving energy.